1. Field of the Invention
The present invention relates to a circularly polarized wave antenna for transmittingxe2x80x94receiving a circularly polarized radio wave, and a communication device using the same.
2. Description of the Related Art
FIG. 6A is a schematic perspective view of a circularly polarized wave antenna contained in a radio wave device. FIG. 6B is a cross sectional view of a part taken along line axe2x80x94a in FIG. 6A. The circularly polarized wave antenna 30 shown in FIGS. 6A and 6B is a circularly polarized wave micro-strip antenna described in Japanese Examined Patent Application Publication No. 7-46762. With the circularly polarized wave antenna 30, transmissionxe2x80x94reception of radio waves in plural different frequency bands is realized. The circularly polarized wave antenna 30 can correspond to plural different systems such as GPS (Global Positioning System) and S-DAB (DAB(Digital Audio Broadcast) using an S band), and so forth.
The circularly polarized wave antenna 30 has the double structure in which MSA (micro-strip antenna) 32 for exciting a fundamental mode (principal mode) is loaded on the upper face of MSA 31 for exciting a higher mode, as shown in FIGS. 6A and 6B, in close contact with and coaxially with the MSA 32.
The higher mode excitation MSA 31 has the configuration in which a circular radiation electrode 34 is formed on the surface of a rectangular parallelepiped dielectric substrate 33. Feed pins (probes for a higher mode) G1, G1xe2x80x2, G2, and G2xe2x80x2 for feeding power to the radiation electrode 34 are inserted into the dielectric substrate 33. The fundamental mode of excitation of MSA 32 comprises a circular radiation electrode 38 formed on the upper face of the columnar dielectric substrate 37. Feed pins (fundamental mode probes) F1 and F2 for feeding power to the radiation electrode 38 are inserted so as to extend through the substrate.
By externally supplying power to the feed pins F1 and F2, the radiation electrode 38 is excited, so that transmission-reception of a circularly polarized radio wave in the fundamental mode can be carried out. When powers are externally supplied to the feed pins G1, G1xe2x80x2, G2, and G2xe2x80x2, respectively, in such a manner that powers in phase with each other are supplied to the feed pins G1 and G1xe2x80x2, and the feed pins G2 and G2xe2x80x2, and powers with a 90xc2x0 phase shift are supplied to the feed pins G1 and G2, the radiation electrode 34 is excited, and thus, transmission-reception of the circularly polarized radio wave in the higher mode can be carried out.
In this patent specification, the fundamental mode is defined as a mode having the lowest resonance frequency in plural set excitation (resonance) modes, and the higher mode is defined as a mode having a resonance frequency higher than the lowest resonance frequency. Reference numeral 40 in FIGS. 6A and 6B designates a center pin for compensating for the symmetry of the fundamental and higher modes.
With the circularly polarized wave antenna 30 configured as described above, transmissionxe2x80x94reception of radio waves in plural different frequency bands can be carried out. On the other hand, there arise the problems that the size of the antenna is increased, since the dielectric substrate 37 is overlaid on the dielectric substrate 33 so as to form plural steps. Furthermore, the circularly polarized wave antenna 30 has a configuration in which power is directed to the radiation electrode by use of the feed pins. With this configuration, problematically, the structure of the antenna 30 becomes complicated. Furthermore, problematically, it is difficult to adjust and set the interval between the respective resonance frequencies in the fundamental and higher modes.
Furthermore, the circularly polarized wave antenna 30 has the following problems. The circuit substrate onto which the circularly polarized wave antenna 30 is mounted is provided with a circuit for driving the circularly polarized wave antenna 30. In some cases, for the purpose of reducing size, the circuit is formed on the back face opposite to the surface having the antenna mounted thereto. In the circularly polarized wave antenna 30, the feed pins are disposed near to the center of the dielectric substrate 31. Accordingly, in the case of the circuit provided on the back face of the circuit substrate as described above, it is difficult to electrically connect the feed pins and the circuit to each other sufficiently, and moreover, there is the problem that patterning the circuit is difficult.
To solve the above problems, the present invention has been devised. It is an object of the present invention to provide a circularly polarized wave antenna which realizes transmissionxe2x80x94reception of circularly polarized radio waves in both fundamental and higher modes, and is small in size, and with which a good circularly polarized wave characteristic can be easily obtained, and to provide a communication device using the same. It is another object of the present invention to provide a circularly polarized wave antenna in which the interval between the respective resonance frequencies in the fundamental and higher modes can be easily adjusted and set, and a communication device using the same.
To achieve the above and other objects, according to the present invention, there is provided a circularly polarized wave antenna which comprises a substantially circular dielectric substrate, a radiation electrode for transmittingxe2x80x94receiving a circularly polarized radio wave formed on the upper face of the dielectric substrate, a fundamental mode feed electrode for feeding power to the radiation electrode to excite the radiation electrode in a fundamental mode, and a higher mode feed electrode for feeding power to the radiation electrode to excite the radiation electrode in a higher mode, the fundamental and higher mode feed electrodes being formed on the side peripheral face of the dielectric substrate and being configured so as to feed the powers to the radiation electrode via capacitive coupling.
Preferably, the radiation electrode is substantially circular, and is provided on the upper face of the dielectric substrate with the center of the radiation electrode being positioned substantially on the center axis of the dielectric substrate. Also preferably, the radiation electrode has such a form as to carry out degeneracy-separation.
Preferably, the radiation electrode is substantially a ring-shape, and is provided on the upper face of the dielectric substrate with the center of the ring of the radiation electrode being positioned substantially on the center axis of the dielectric substrate, and the non-electrode portion enclosed by the ring-shaped radiation electrode comprises a frequency setting portion for adjusting and setting the interval between the respective resonance frequencies in the fundamental and higher modes.
More preferably, a concavity or through-hole is formed in the non-electrode portion enclosed by the substantially ring-shaped radiation electrode in the dielectric substrate.
According to the present invention, there is provided a communication device which includes the circularly polarized wave antenna described above.
According to the present invention having the above-described constitution, when power is supplied from the fundamental mode feed electrode formed on the side peripheral face of the substantially columnar dielectric substrate to the radiation electrode formed on the upper face of the dielectric substrate via capacitive coupling, the radiation electrode is excited in the fundamental mode, so that transmissionxe2x80x94reception of a circularly polarized radio wave in the fundamental mode can be carried out. Moreover, when power is supplied from the higher mode feed electrode to the radiation electrode via capacitive coupling, the radiation electrode is excited in the higher mode, so that transmissionxe2x80x94reception of the circularly polarized radio wave in the higher mode can be carried out.
The radiation electrode has both of the functions as a radiation electrode for the fundamental mode and as a radiation electrode for the higher mode. Accordingly, in contrast to the case in which the radiation electrodes for the fundamental mode and the higher mode are separately provided, the size of the antenna can be prevented from increasing or can be reduced in size.
Furthermore, the circularly polarized wave antenna of the present invention is configured so that power is supplied from the feed electrodes to the radiation electrode via capacitive coupling. Accordingly, a good circularly polarized wave characteristic can be obtained in each of the fundamental and higher modes, in contrast to the case of the direct feeding using the feed pins.
Moreover, in the case in which the radiation electrode has a substantially ring shape, the non-electrode portion enclosed by the radiation electrode is provided, and the concavity or through-hole is formed in the non-electrode portion in the dielectric substrate, the interval between the respective resonance frequencies in the fundamental and higher modes can be easily adjusted and set by changing the size of the non-electrode portion and the sizes of the concavity or through-hole. Thus, the adjustment and setting of the interval between the respective resonance frequencies in the fundamental and higher modes can be simply achieved, and can be set at a predetermined interval specified by specifications or the like.